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How An Ejector Works

Principle of Operation of Ejectors

Let’s explore how an Ejector works. Firstly, it is worth noting that Ejectors are also known as Eductors, Surface Jet Pumps, Venturi’s or Velocity Spools. The operating principle is common to all, regardless of name.


Based upon Bernoulli’s Principle, as the velocity of a fluid increases, its pressure decreases, and vice versa.


An Ejector works by accelerating a high pressure stream (the ‘motive’) through a nozzle, converting the pressure energy into velocity. Around the nozzle tip, where velocity is highest, a low pressure region is created. This is often called the suction chamber of the Ejector. Where the pressure in this region is lower than the pressure of the suction fluid connected to the Ejector side-inlet or ‘suction branch’, it will be entrained/sucked into the body of the Ejector. The two fluid streams then travel through the diffuser section of the Ejector, where velocity is decreased as a result of the diverging geometry and pressure is regained.


Importantly, the low pressure suction stream experiences a pressure increase/compression, whilst the motive stream sees a decrease in pressure, as some of its energy has been used to ‘do work’ on the suction stream. The resultant discharge pressure is therefore somewhere between the motive and suction pressures.

Ejectors are pipeline mounted devices and can be manufactured in almost any material to suit the process conditions. They have 3 connections; Motive, Suction and Discharge.


Learn about the Joule-Thomson Effect and how it affects temperature of fluids through an Ejector.

Ejectors are simple, static devices that use the energy within a high-pressure motive fluid (Gas or Liquid) to entrain and compress a low-pressure suction fluid (Flare Gas) to an intermediate discharge pressure.